In various types of machinery and powered equipment, such as a table saw, it is desirable to preclude inadvertent or unauthorized operation of the switch and hence the equipment controlled thereby. In the prior art, of which I am aware, various means have been provided to preclude such unauthorized operation.
For example, the switch may be of the simple toggle type, and a u-shaped bracket may have its bight portion secured to the housing, such that the legs of the bracket extend on respective sides of the toggle. Each of the legs may have a hole formed therein, and with the toggle in its down or "off" position, a simple padlock may be inserted between the holes in the legs of the bracket and locked therein. Movement of the toggle into the "on" position will thereafter be precluded, until the padlock is removed.
Additionally, a key may be installed integrally on the machine, adjacent to a separately-mounted switch actuator, and removal of the key will preclude operation of the switch actuator from an "off" to an "on" position. These mechanisms are usually arranged, upon insertion of the key, to remove an internal barrier to movement of the switch actuator to its "on" position.
Additionally, the art has resorted to a variety of lock buttons or other locking members mounted within the switch actuator. For example, the lock button may comprise a bifurcated plug member having a pair of fixed prongs inserted into a receptacle in a rocker-type switch. The plug member may be removed to preclude pivotal movement of the rocker switch from its "off" position into its "on" position. Others in the art have used a similar pronged-type of removable lock button for a "pull on/push off" switch, wherein the actuator may be provided with an enlarged outer operating portion to facilitate its manipulation. Still others have resorted to a lock button in conjunction with a pistol-grip type of handle provided with a trigger switch; the lock button must be continually depressed to enable the switch to be actuated by the trigger. In this arrangement, the lock button may be removed to prevent an inadvertent or unauthorized use of the switch. Finally, the commercial art has disclosed an arrangement, wherein, the switch is completely inaccessible to the operator upon removal of the actuator.
The Peterson U.S. Pat. No. 4,107,484 is also illustrative of the development of the art. In this patent, a key-type of actuator is used with a rocker-type of switch. The key may be inserted into its keyway and then rotated for proper orientation with respect to the rocker switch. When so alined, the key may be pulled for moving the switch into its "on" position and pushed for moving the switch back into its "off" position. The key may be withdrawn from the switch only in the "off" position of the switch.
These prior art disclosures and structures are relatively complicated and sophisticated, hence expensive to manufacture and to assemble into a power-operated machine. Additionally, the stationary prongs of the plug-type keys may break off after repeated and extensive insertions of the keys into the switch actuator. Moreover, the switch may still be accessible, even after removal of the lock button, and any internal blockage within the switch may conceivably be over-ridden by the application of heavy manual pressure on the accessible switch.